In 1976, a sodium fluoride (NaF) mouthrinse study was started in Biddeford, Maine, a non-fluoride area. Baseline dental examinations (DMFS Index) were made of 825 children in grades 5-7 attending seven schools in the community. Participants were randomly divided into three groups. Under teacher supervision, they rinsed either weekly with a 0.2% NaF solution or a 0.1% sodium chloride solution (Placebo) or daily with a 0.05% NaF solution. Treatments were carried out for three school years. Follow-up dental examinations were scheduled annually to compare the anti-caries effectiveness of the two fluoride mouthrinse procedures. The third and last year of treatments and final examinations were carried out in 1979.